304 



THE MUSCLES 



Insertion. — (1) The lesser tul)erosity of the humerus, and the part of the shaft 

 inmu'diati^'ly below it; (2) the front of the capsular ligament of the shoulder-joint. 



Structure. — Its origin is by fleshy fibres from the surface of the ))one, and also 

 by bi{)enniform bundles from the upper and lower surfaces of three or four septa 

 which are attached to the transverse ridges upon the venter scai)ul8e, so that the 

 whole muscle has a multipenniform arrangement. The fibres converge upwards 

 and outwards upon a strong tendon which is hidden by fleshy fibres to within a 

 short distance of its insertion, the lower part of which is also fleshy. A bursa 

 intervenes between the tendon and the base of the coracoid process, and is usually 

 in connection with the shoulder-joint. 



Nerve-supply. — From the posterior cord of the bi'achial plexus (through the 

 fifth and sixth cervical nerves), by the short and part of the lower subscapular 

 nerves. They enter the front surface of the muscle, the former near its upper, the 

 latter near its outer border. 



Action. — It is the chief internal rotator of the humerus; at the same time it 

 adducts it after it has been elevated. It also has an important influence in 



Fig. 269. — Front View of the Scapular Muscles. 



CLAVICLE — 

 CORACOID PROCESS 

 Supra-spinatus 



Subacapularis 



Teres major 

 Latissimus dorsi 



Coraco-brachialiB and short 

 head of biceps 



Peetoralis major 



strengthening the shoulder-joint by drawing the head of the humerus towards the 

 glenoid cavity. 



Relations. — Its anterior and internal face forms the greater part of the posterior 

 wall of the axilla, and is in contact with the serratus magnus, the short head of the 

 biceps, and the coraco-brachialis, the axillary vessels with many of their branches, 

 the brachial plexus and its branches, the lymphatic glands and vessels; its outer 

 border lies in contact with the teres major, the posterior circumflex and dorsalis 

 scapula? vessels, and the circumflex nerve; behind lie the long head of the triceps 

 and the teres minor muscle, and the bursa which intervenes between its tendon and 

 the capsule of the shoulder-joint. 



Variations. — Occasionally a separate slip arises from the axillary border of the scapula, and is 

 inserted into the capsule of the shoulder-joint or into the humerus. 



6. TERES MAJOR 



The teres major — named from its somewhat cylindrical shape and its size — is 

 a thick ril)l)on-sliaped muscle. 



Origin. — (1) The oval facet which occupies the lower third of the axillary 

 border of the infraspinous fossa; (2) the infrasi)inous fascia and the intermuscular 



